Discharge device



Filed March 16, 1942 Inven'for: CGT'L Dimel,

b WW

His Ahforneg.

Patented Nov. 9, 1943 97 "unit-sin] STATES PATENT orrics j;

Carl Deimel, Berlin-Charlottenburg, Germany, assignor to General Electric Company, a cor.-

poration of New York Application March 16,1942,'"Serial No. 434,968 a In Germany December 23,1940! scams: (01. 250-215) 3 My invention relates toglow dischargevdevices of the type comprising closely spaced electrodes of large surface'co'ated with-alkaline earth metal, such as wire orsheet metal electrodes of iron, nickel, or aluminuni. These alkaline earth metal coatings make 1 itpossible to attain low starting and operating potentials and are readily produced by the dissociation of azides, carbonates or nitrates of these metals which compounds are applied to the electrode surfaces. The alkaline earth metal coatings produced from carbonates or nitrates give particularly low starting and operatin voltages, probably because they are purer than thealkaline earth metal coatings produced from azides. The greater purity of the electrode layer entails also apermanent purity of the icnizable gas with which the device is filled. Frequently, an appreciable time elapses,which may be seconds after application of the starting potentialto such devices'before ignition oi the discharge occurs. This delay in starting is very disadvantageous in a goodmany applications of such devices; for instance, it is disadvantageous when the devices are used for signalling or relay purposes. Iniact,

such delay may make'the devices useless for such P ses.

Radioactive materials areuseful for minimizing the-delay in starting'of such glow discharge devices. I have observed, however, that when such materials are present inthe form'of compounds f mixed'with the alkaline earth metal on the electrodes of the device, the glow discharge'does not appear uniformly over the coated surface of the electrodes, which is disadvantageous when the device is used as a lamp, and the starting and operating voltages of'the device are increased.

An object of my invention is to provide a glow discharge device having alkaline earth metals produced from the carbonates or nitrate of these metals on the electrodes of the device together with radioactive material which device starts not later than ti of a second after the application of the starting potential thereto and which retains I the starting and operating voltages characteristic of such devices having no radioactive material on the electrodes thereof. Another object of my invention is to provide a method of manufacturing such devices. Further objectsand advantage of my invention will appear to those skilled in the art from the following detailed description thereof. o

I have discovered that the above objects are attained when the radioactive material is present in the form of metal which is finely and uniformly distributed in the coating of alkaline earth metal on the electrodes of the device and when the radioactive metalis produced on the electrode'by adding a small amount, preferably less than 0.1 per cent by weight, of a suitable compound thereof, such as radium carbonate or nitrate, to: the alkaline earth metal carbonates or nitrates used for producing the alkaline earth metal layer or coating on the electrodes, which radioactive metal compound is decomposedtogether with the alkaline earth metal compound, to the form of metal on the surface of the electrode. q

The method of my'invention makes possible a selection of the'quantity of the radioactive metal with respect to the alkaline earth metal, so that the quantity'most suitable for a particular use of the device may be applied to the electrodes. Thus,

.thea'pplication of excessive amounts of radioactive metal may be avoided and, since a relatively small quantity of atoms of the radioactive element in the finishedelectrode layer willsufllce toprevent the delay in starting of the discharge, the cost of manufacture of discharge devices comprisingradioactive materials is reduced to a minimum; a '1 As the main material' for the electrode coating I prefer an alkaline earth carbonate or nitrate, or a mixture of several uch carbonates or nitrates,

for instance a mixture of barium and strontium.

carbonates. To themain material I prefer to admix, withthehelp of a suitable elutriating liquid suchas methyl alcohol or acetone, and with the addition of a binder such as a nitrocellulosesolution,a slight amount of a corresponding compound of a radioactive element. Thus, radium carbonate may be admixed to the alkaline earth carbonate or carbonates, whereupon the suspension produced in this manner is thoroughly ground. The quantity of added radioactive compound is so measured that, in orders of magnitude, one radioactive atom is added to a million alkaline earth atoms. The mixture is then sprayed on the-electrode surface or is applied t the latter by electrophoresis. v

A uniform distribution of the particles of the radioactive compound within the structure of the particles of the alkaline earth metal compound, or compounds is thus produced on the electrodes The electrodes are then heated to a glowing temperature in vacuo, in the well known manner. The envelope of the device is then filled with a suitable gas, such as neon, or argon, under a pressure of about 20 to 50 mm. Hg, and the products of decomposition which have remained on the electrodes from the preceding heating are further destroyed by producing dislays of the gaseous electric discharge type come-H.

prising a bimetallic electrode and used in the starting circuits of ultraviolet and fluomsccniry,

lamps of the positive column discharge type having electrodes trodes in series across the terminals of a current source to heat said electrodes; to a.- 'd.is'-

rupted when the electrode 4 flexes back to its orginal, spaced position with respect to the electrode 3 a short time after the glow discharge has been short circuited by the engagement of the electrodes. The electrodes 3 and 4 are provided with a mixture of alkaline earth metal and radium in accordance with my invention.

What'I claim as new and idesiie tn secure by Letters Patent of the United States" is: 10

mg coacting electrodes severally surfaced with layerscomprising pure alkaline earth metal per- 1. A gaseous electric glow discharge comprismeated with radioactive atoms uniformly diswhich require preheating. Such relays are used to connect the lamp elec-' charge sustaining temperature and to break-121w series connection between said electrodes when.

they have attained such temperature. Fast starting of the discharge in; relays used in: such lamp circuits is highly desirablepin" order to minimize the time between the applicationfcf potential to the lamp scircuit'and th'e: emission of. light by the-lamp.v Uniform coverage? of the glawdischarge over-the electrodes of. the relay is likewise-desirable for the samereason; since the bimetallic electrode is thus-quickly heated by the glow discharge and flexes into engagement -witlranother electrode inthe rel'myto extinguish the discharge between the .electrodesaand topermit a heavyheaterucurrent to flow through the seriesconnected: electrodes of the lamp Relays of this type are" commonly called switches in the lampart andva species thereof is disclosed in the copendmg'application Serial No. 400.645,..fi-led July" 194-1, inventor Leo R. Peters, which applica-tion-is"-'assignedto the assignee of the present application: The switch disclosed: in the cope-riding applicatiozrcompris'es a sealed envelope containing an i'onizable gaseous atmosphere and; normally spaced cooperating electrodes including a stationary electrode and a bimetallic electrode constructed andrzarra'nged to make contact 'with" thevstationary electrode and thus to extinguishr-tho discharge?- between said elicctrodes whcmheated: by said discharge. Metals of low work function; such as: the' alkaline eartnmetals, on the switch electrodes make possible .thefabricationsof switches capable of start:- img and operatingon commercial voltages of I10 and=220voltsh Inthe. drawing accompanying and. formingpar't of this speci'flcationl' have shown, :irr arperspecthe view) a switch of the type described above wl'rtch comprisesa sealed "envelope t containing an ionized gas and having a stemr l supporting electrodes 3 and 4. Though initially separated, theel'ectrodes'engageeach other to permit- 1a heavy current towfio'w through: the-switch when the bimetallic electrode 4 is heated 'by aglow discharge betweenfsai'cl electrode -4 'and the stationary electrode 3, The hea'vycurrentzis intert'ributed therein, in proportions of the order of a minor fraction'ofa per cent of radioactive metal to alkaline earth metal.

2. The method orminimizing the starting time without increasing the starting and operating voltage of gaseous electric discharge devices of the glow discharge type having alkaline earth metal; on the: electrodes thereof which: comprises the steps of first mixmamaterialfromthetgrolrp ccnsist'ing'of the carbonates and-minutes of:fthe alkaline earth metals: witha. corresponding compound of radium, applying vraid; mixture to. said electrodes and then decomposing compounds to produce a mixture of radiwn'andsalkaline earth metal oncsaid 'electrodmz: w I a 3. The method of minimizingthe startingetime without increasing, the. starting-can't operating voltage of gaseouselectric dischargeidevicesxoi the glow discharge type having alkaline earth metal: on the electrodes; thereof which comprises the steps of first mixiing thescarbonate of an alkaline earth metal withradituni carbonate; applying, said mixture toisaid elactrodes and then decomposing.said':compounds: to produce a mixture of radium and alkaline earth; metal on sa d l t d v s 4. The method of miniim'migxthc' starting time without increasing the staxtmg andrr operating voltage: of gaseous electrioadi'scmrgadevices of the glow. discharge i type 'hmng; vallcalinez earth metal onthe electrodes'thoreafi which comprises the steps: of first mxing 'thenitrate. at 2ma1kaline earth metal with radium nitrate, applying'suid mixture: to said electrodes and than decomposing and alkaline-earth metal on saidelectrodes; 

